Abstract 2013: Soil erosion by water is the major source of soil and water quality degradation worldwide. Especially in mountainous landscapes, water erosion is a serious problem, which reduces agricultural productivity and downstream water usability. The most crucial factor controlling erosion and transport of sediments in those landscapes is the local land management. We investigated farm management practices in a mountainous watershed of South Korea with respect to influences on soil erosion by water and to identify effective erosion control measures. Dryland agricultural areas in South Korea are dominated by row crop cultivation, which makes soils highly susceptible to monsoon rainfall and overland flow because of heavy conventional herbicide applications and resulting low groundcover. “Environmentally friendly farming” practices, on the other hand, avoid the use of herbicides and pesticides and can increase weed development and soil cover. We used the RUSLE erosion model to assess the effect of such farming systems on soil loss in comparison to conventional farming. We found lower erosion for organic radish fields due to increased weed coverage, but increased soil loss for organic potato because of reduced crop yields. However, for both conventional and organic farming, the annual soil loss rates exceeded tolerable erosion levels. Row crop fields require better protection by effective management measures, such as cover crop cultivation and residue mulching. These measures, however, only control soil loss on-site. They do not address the fate of eroded sediments outside of fields within the landscape. In order to investigate the transport pathways of those sediments from field sites into the stream network, we applied the model EROSION 3D over the entire catchment. Our results reveal locations of erosion hot spots, and demonstrate the sediment retention by landscape elements such as riparian forests, fallow fields, and plantations of perennial crops. Since the water quality monitoring we conducted during the last years demonstrated continuously high sediment concentrations and phosphorus loads in streams for most of the monsoon rain events, additional best management practices are required to reduce the transport of sediment from fields into streams and to the reservoir. Artificial mats in field margins, densely vegetated marginal strips, and basins that function as sediment traps provide possible measures to control off-site erosion in the study area. The studies will be extended in a postdoctoral project during cohort 2 to evaluate erosion and sediment transport throughout the Soyang Watershed with the goal of estimating sediment delivery to Soyang Lake currently and in land management scenarios.
Keywords: crop cultivation, soil loss, phosphorus, water quality, best management practices
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